Fish tank



FIG. 1 is a perspective view showing my new design;

FIG. 2 is a front plan view thereof;

FIG. 3 is a back plan view thereof.

FIG. 4 is a left plan view thereof;

FIG. 5 is a right plan view thereof; and,

FIG. 6 is a downward plan view thereof.

The broken lines shown in FIGS. 3, 4, 5 and 6 represent portions of the fish tank that form no part of the claimed design. 

CLAIM The ornamental design for a fish tank, as shown and described. 